1. Field of the Invention
The present invention relates to a method utilizing a radionavigation system in a routine way to locate a reference point on a first mobile object and making it possible, without modifying the radionavigation system, to:
locate on board the first object a plurality of second mobiel objects linked to the first object or not, in real time;
orient the direction defined by each of these second objects and the reference point on the first object on board the latter in real time;
orient a reference direction linked to the structure of the first mobile object in the case where acoustical, optical or radio-electrical systems linked to the first object make it possible to define the orientation of the second mobiles relative to the reference direction of the first mobile; thisis also valid if the aforementioned acoustical, optical or radio-electrical systems make it possible to locate the second objects in a reference system linked to the structure of the first mobile. This operation is effected on board the first mobile and in real time.
2. Description of the prior art
Radionavigation systems as used nowadays for locating mobile objects such as ships or the like usually employ a radionavigation system providing for a circular or hyperbolic type location method. The principle of locating one or more autonomous mobile objects relative to one or other of the location systems does not raise any major problem, modification of the relative position of one or other of the autonomous mobiles, or even of their orientation relative to a reference direction, involving only an exchange of their respective position as determined relative to a common reference radionavigation system under the normal conditions for utilization of the latter.
If it is necessary to define the orientation of the direction formed by a non-autonomous second object and at least one reference point on the autonomous first object, the non-autonomous second object not being itself able to calculate and communicate its position to the first mobile object, which is autonomous, the solutions proposed until now usually entail defining the angular offset between this direction and a reference direction linked to the first mobile by acoustical, optical or radio-electrical methods using the first mobile as a reference.
Although the angular offset can be defined with satisfactory precision, the same cannot be said of the absolute orientation, which depend on the accuracy with which the reference direction is known. In the case of ships, this is defined by a gyrocompass which can introduce errors of as much as one degree due to changes in the position of the ship, especially in the case of three-dimensional seismic investigations.
It is, of course, out of the question to render the second mobile object autonomous, that is to say capable of establishing its own position and communicating it to any other mobile, because of the prohibitive cost and the fact that it is virtually impossible to do so for material or technical reasons, where the second mobile object is of low buoyancy and cannot carry bulky and heavy equipment. This difficulty is accentuated in the presence of a plurality of non-autonomous second mobile objects, as in the case of marine geophysical prospecting using a plurality of towed cables (known as "multistreamer" prospecting).
In the case where a circular location type radionavigation system with active mobiles is used, the number of mobiles that can be accepted is limited and the system must be configured to accep these mobiles, imposing very severe limitations since this is not always possible.
An object of the invention is to remedy the aforementioned disadvantages by providing a method and a system for locating and orienting a first direction linked to the position and orientation of an autonomous first mobile object and a second direction defined by a non-autonomous second mobile object and at least one reference point on the first mobile object and involving little expenditure on navigation equipment.
Another object of the present invention is to provide a method and a system for locating and orienting a first direction linked to the position and orientation of an autonomous first mobile object and a second direction defined by a non-autonomous second mobile object and at least one reference point on the first mobile object using an acoustical, optical or radio-electrical system defining the position or the orientation of the second mobile in a reference system linked to the first mobile.
A further object of the present invention is to provide a method and a system for locating and orienting a first direction linked to the position and to the orientation of an autonomous first mobile object and a second direction defined by a non-autonomous second mobile object and a reference point on the autonomous first mobile using a radionavigation system, the method and the device of the invention being totally transparent to the radionavigation system and therefore not requiring any modification thereto.
A final object of the present invention is to provide a method and a system for locating and orienting a first direction defined by the axis of an autonomous first mobile object and a non-autonomous second mobile object of great precision.